Two curves on a highway have the same radii. However, one is unbanked and the other is banked at an angle ɵ. A car can safely travel along the unbanked curve at a maximum speed v under conditions when the coefficient of static friction between the tires and the road is μs = 0.787. The banked curve is frictionless, and the car can negotiate it at the same maximum speed v. Find the angle ɵ of the banked curve.

For unbanked curve, centripetal force is provided by friction and for banked curve, centripetal force is provided by component of reaction from the ground.

centripetal force = m v² / r, m is mass, v is velocity and r is radius of curve.

friction force (maximum) = μ mg, μ is coefficient of friction,

for motion on unbanked curve

m v² / r = μ mg

v² = μ gr

=.787 x 9.8 x r

= 7.712 r

In case of motion on banked curve having angle of banking θ

If R be the ground reaction

R cosθ = mg

Rsinθ = centripetal force

= m v² / r

Dividing the two

Tanθ = v² / rg

= 7.712 r / 9.8 r

tanθ =.787

θ = 38 degree.